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'fairly' novel design

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GeoffBird View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GeoffBird Quote  Post ReplyReply Direct Link To This Post Posted: 26 June 2017 at 11:19pm
Ah, the name came from deep in my unconscious :-) Radnabel





Edited by GeoffBird - 26 June 2017 at 11:28pm
Right Time - Right Place - Wrong Speed
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob walton Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2017 at 9:38pm
I am thinking of popping round to your meeting tomorrow in Shrewsbury just to see what the crack is. i will bring my bike. 

cheers,

bob
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Post Options Post Options   Thanks (0) Thanks(0)   Quote atlas_shrugged Quote  Post ReplyReply Direct Link To This Post Posted: 02 July 2017 at 10:23pm
I enjoyed riding your bike around at Shewsbury. It felt very stable and I liked the very good turning capability. Thanks for bringing it along.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob walton Quote  Post ReplyReply Direct Link To This Post Posted: 02 July 2017 at 11:21pm
It's nice of you to say so. I must admit that was a fascinating experience for me. I have never been up close to bikes that before, and I really learnt a lot - friendly atmosphere, and the sun even came out. I can see I am a bit of a beginner here. I'll just have to raise my game ......again! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GeoffBird Quote  Post ReplyReply Direct Link To This Post Posted: 03 July 2017 at 11:26am
Glad you made it to an event Bob. Sorry we couldn't be there. We had a bad night's sleep and couldn't find the energy to get up early...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob walton Quote  Post ReplyReply Direct Link To This Post Posted: 04 July 2017 at 12:11pm
By the way didn't really think the Radnabel bike looked the same. The headset was the normal way round with direct steering. Maybe my front end is 'actually' novel, rather than 'fairly' novel?? Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2018 at 11:16am
I can attest that negative steering angle (if you add remote steering, of course) results in very nice handling characteristics, a small negative angle is likely better than Burrows-suggested 90deg steering because of a unique combination of positive trail and *negative* wheel flop.
 
To be fair, you can have a similar effect by installing a strong return to center spring - that is what, actually, negative angle does in a way.
 
It does come with negatives like having to incorporate lots of negative offset and hence being unable to use conventional suspension forks, plus braking hard or hitting a pothole may bend your forks unless you make them really strong.
 
It has much more merit for MBB actually, but making remote steering on MBB is really, really hard due to huge 'pedal feedback' forces involved.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob walton Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2018 at 12:55pm
Adding a spring to the steering isn't the same as using a negative rake. The spring force will depend only on the angle the wheel is turned to the side. The 'correcting' force here depends on how off balance you are, and it turns the steering to correct the imbalance. It's way better than using a spring!

Also, the forks don't need to be mega-strong as you suggest. There isn't as much weight on the front wheel as there is on a normal bike because most of the rider's weight is on the back. There is much less weight shift when you brake too. That means you never finish up with all your weight on the front wheel when you brake hard. And the forks are shorter than on a normal bike so the bending moment (force x lever arm) tends to be smaller. These three effects mean that the forks don't need to be extra strong. In fact, I used forks from a kids bike and I have gone over lots of pot holes without braking anything. 

If you did want suspension, do it like this...


This is an off-the-shelf swing arm and off-the-shelf shockers, just like a normal twin shock rear suspension, but fitted to the front with a big pivot. Everything is completely conventional Confused


Edited by GeoffBird - 06 March 2018 at 9:55pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Balor Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2018 at 1:47pm
Originally posted by bob walton bob walton wrote:

Adding a spring to the steering isn't the same as using a negative rake. The spring force will depend only on the angle the wheel is turned to the side. The 'correcting' force here depends on how off balance you are, and it turns the steering to correct the imbalance. It's way better than using a spring!
 
I'm sure if I follow... which 'correcting force' do you have in mind? Trail and camber torque? Those are present in conventional designs, this is why DF bicycles are self-stable. Negative wheel flop? As much as I understand, it is simply a case stable equilibrium, hence - 'return to center' force, unlike unstable equilibrium of conventional wheel flop.
Weight distribution? Negative offset and some tiller does not help, actually.
Can your design be self-stable like DF bike on this video?
https://www.youtube.com/watch?v=Zt7J0dly70M
 
Originally posted by bob Walton bob Walton wrote:

Also, the forks don't need to be mega-strong as you suggest. There isn't as much weight on the front wheel as there is on a normal bike because most of the rider's weight is on the back. There is much less weight shift when you brake too. That means you never finish up with all your weight on the front wheel when you brake hard. And the forks are shorter than on a normal bike so the bending moment (force x lever arm) tends to be smaller. These three effects mean that the forks don't need to be extra strong. In fact, I used forks from a kids bike and I have gone over lots of pot holes without braking anything. 
 
Yea, admittedly those are not a problem for your particular implementation (lwb). I'm was talking on general principle.
 
Originally posted by bob Walton bob Walton wrote:


If you did want suspension, do it like this...
This is an off-the-shelf swing arm and off-the-shelf shockers, just like a normal twin shock rear suspension, but fitted to the front with a big pivot. Everything is completely conventional Confused
 
Well, extending this logic, every bike is just conventional pieces of metal fitting together :).
I mean you cannot just take off the shelf telescoping fork and expect it to work.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob walton Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2018 at 3:56pm
Yes, it balances like a normal bike. The way this happens is actually quite complicated because there are gyroscopic and other dynamic forces at work here too, but I will try to explain in simple terms. If you let go of the handlebars on a normal bike at standstill, the steering will tend to turn fully to one side (Wheel flop it's called). But on a bike with negative rake it will tend to straighten. This is a stabilising effect because you want the wheel to point the way you are going. But if you are going round a corner of constant radius at constant speed, the steering has to be turned slightly to one side. On a bike with a negative rake the steering will not try to straighten the way it would if it was centred by a spring. And you don't want it to straighten because you are going round a corner of constant radius. 

To prove that it works watch this video...
https://www.youtube.com/watch?v=lgJjgRtKNT4&feature=youtu.be
... where I ride an earlier version of the same bike no hands. You can't normally do that on a recumbent.

Yes, any bike is just a bunch of metal parts. But that's a bit like saying a face is just a bunch of features. It's the way the the features are arranged on the face that distinguishes one from another. Wink


Edited by bob walton - 03 March 2018 at 8:21pm
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